The ability to manipulate individual atoms for use in nanotechnology components continues to develop. Some of these developments are in the field of materials and specifically atomically thin materials which may use a single molecular component or selected combinations of molecular components. One example of such a material is graphene which is a two-dimensional aromatic carbon polymer that has a multitude of applications ranging from electronic memory, electrical storage, composite enhancement, membranes and the like. Other atomically thin materials are believed to have their own beneficial properties.
One non-limiting example of an atomically thin material is graphene. A graphene membrane is a single-atomic-layer-thick layer of carbon atoms, bound together to define a sheet. The thickness of a single graphene membrane, which may be referred to as a layer or a sheet, is approximately 0.2 to 0.3 nanometers (nm) thick, or as sometimes referred to herein “thin.” The carbon atoms of the graphene layer define a repeating pattern of hexagonal ring structures (benzene rings) constructed of six carbon atoms, which form a honeycomb lattice of carbon atoms. An interstitial aperture is formed by each six carbon atom ring structure in the sheet and this interstitial aperture is less than one nanometer across. Indeed, skilled artisans will appreciate that the interstitial aperture is believed to be about 0.23 nanometers across at its longest dimension. Accordingly, the dimension and configuration of the interstitial aperture and the electron nature of the graphene precludes transport of any molecule across the graphene's thickness unless there are perforations.
Recent developments have focused upon graphene membranes for use as filtration membranes in applications such as salt water desalination. One example of such an application is disclosed in U.S. Pat. No. 8,361,321 which is incorporated herein by reference. As these various uses of graphene and other atomically thin materials develop, there is a need to manufacture materials and supporting substrates which have nano or micro size apertures or holes.
Nanoporous membranes which have a pore size of 0.1-10 nm are difficult to manufacture because the membrane must typically be extremely thin to allow such a small pore size to persist throughout the membranes' thickness. Accordingly, the membrane bearing the pore must be supported on a thicker porous substrate to embue the final composite membrane with sufficient mechanical strength.
A current method of making such a composite membrane uses perforated graphene (thickness about 1 nm) as an active membrane material and a porous polycarbonate film (thickness about 5-10 μm) as the supporting substrate. These two layers are mated to on another after the holes in each are already made. The holes in both substrates are not registered or aligned with one another, hence flow through the composite membrane is limited by the statistics of overlapping holes. In other words, flow through the composite membrane is limited based on the random alignment of the holes in the graphene membrane material coincidentally aligning with the holes of the porous polycarbonate film
The mating of perforated atomically thin materials, such as graphene, and porous polycarbonate films to create composite membranes for nanofiltration are believed to provide an improvement over other filtration type membranes. Other nanoporous membranes are made of thicker polymer films with tortuous paths that demonstrate nanoscale exclusion, but they typically have extremely low permeability as a result of their thickness. Therefore, there is a need in the art to provide a nanoporous membrane with an atomically thin material layer and a polymer layer that have aligned concentric holes. Moreover, this is a need in the art for a nanoporous membrane which provides for concentric holes through the atomically thin material layer and the polymer film layer wherein the holes through the polymer film layer are substantially larger in diameter than the diameter of holes through the atomically thin material layer.